Great advances have been made in semiconductor technology in the last few years due to the discovery of new fabrication techniques, the smaller size of geometrical features on semiconductor devices and the greater accuracy in placing certain geometrical features on semiconductor devices. In this way, various integrated circuits have been developed in which the circuit elements including semiconductor circuit elements are made directly on the semiconductor material. As time passed and fabrication techniques improved, the density of circuit elements has increased. Tolerance limits have become more demanding, geometrical features smaller and more precise and placement accuracy more precise.
The revolution in semiconductor technology has been most apparent in silicon semiconductor technology. Most semiconductor devices are made with this material. It is readily available in large boules, has excellent mechanical properties, can easily be purified and is relatively well understood as far as semiconductor properties are concerned.
Semiconductor technology has advanced to such a state with silicon that devices with design parameters of about one micrometer are being manufactured. Memories with storage capacities of about 256,000 bits plus associated circuitry are being made on silicon chips with area of about one square centimeter. Other examples are available to show the large advances that have been made in silicon technology in the last few years.
In fabricating such devices, it would be highly advantageous to have an etching procedure which can be controlled as to etch rate, area to be etched and geometrical shape to be etched. Such an etching procedure is usually referred to as an anisotropic etching procedure. Such a procedure would be useful for making channels, via holes, mirrors, lenses, diffraction gratings and in the separation of individual chips on a semiconductor wafer.
Photoelectrochemical etching of III-V semiconductor compounds has been described in a variety of publications including U.S. Pat. No. 4,389,291, issued to P. A. Kohl et al on June 21, 1983; U.S. Pat. No. 4,399,004, issued to R. R. Buckley et al on Aug. 16, 1983; U.S. Pat. No. 4,404,072, issued to P. A. Kohl et al on Sept. 13, 1983; and D. Lubzens, "Photoetching of InP Mesas for Production of MM-Wave Transferred Oscillators," Electronics Letters, 13, page 171 (1977).